1. Field of the Invention
The present invention relates to a polymer scale deposition preventive agent for use in polymerization of a monomer having an ethylenically unsaturated double bond, and a process for producing a polymer using the same.
2. Description of the Prior Art
Heretofore, processes for polymerization of a vinyl monomer are known, such as suspension, emulsion, solution, gas phase and bulk polymerization processes and the like. In any of these polymerization processes, polymer scale is liable to be deposited on the areas with which the monomer comes into contact, such as inner walls, stirring equipment and so on of a polymerization vessel.
The deposition of polymer scale results in disadvantages that the yield of the polymer and cooling capacity of the polymerization vessel are lowered, and that the polymer scale may peel off and mix into a polymeric product, thereby impairing the quality of the product. In addition, removal of the deposited polymer scale is very laborious and time-consuming, and since the polymer scale contains unreacted monomers (vinyl chloride and the like), it is accompanied by a risk of causing physical disorders in the operators, which has been a very serious problem in recent years.
For preventing polymer scale deposition on the polymerization vessel inner wall and so forth, methods have been known, for example, a method in which a polymer scale deposition preventive agent comprising a polar organic compound such as amine compounds, quinone compounds, aldehyde compounds, etc. is applied to the polymerization vessel inner wall and so on and a method in which such compounds are added to an aqueous medium in which suspension polymerization is carried out (Japanese Patent Publication (KOKOKU) No. 45-30343).
However, according to these methods, although the polymer scale deposition preventive effect is exhibited while polymerization is repeated for up to about 5 or 6 batches, the effect diminishes if the number of repeated batches of polymerization exceeds 5 or 6 (that is, the scale deposition preventive effect is poor in durability). The disadvantage is emphasized particularly where a water-soluble catalyst is used for polymerization, and, therefore, these methods are unsatisfactory industrially.
For overcoming the above disadvantage, Japanese Pre-examination Patent Publication (KOKAI) No. 53-13689 proposes a method in which the inner wall, etc. of a polymerization vessel are coated with a polymer scale deposition preventive agent comprising a condensation product of an aromatic amine compound as an effective constituent. Where the polymer scale deposition preventive agent is applied to the areas with which monomers come into contact, such as the inner wall surface of a polymerization vessel, it is possible to repeat about 100 to 200 batches of polymerization without causing deposition of polymer scale on the areas located in the liquid-phase region inside the polymerization vessel. Besides, even in the case where a water-soluble catalyst is used, deposition of polymer scale in the liquid-phase region is similarly prevented.
However, there is a drawback that polymer scale deposition may occur on the areas around the interface between the liquid phase and the gas phase located at the upper section of the interior of the polymerization vessel.
Once polymer scale deposition occurs on the areas around the interface between the gas and liquid phases, the deposited scale will grow gradually as polymerization runs are repeated, and at last it may peel off to be incorporated into a polymeric product. When the polymeric product with the polymer scale thus mixed therein is processed into formed products such as sheets or the like, the polymer scale causes generation of many fish eyes in the formed products and thereby lowers seriously the quality thereof.
Besides, when the polymeric product is worked into a formed product such as sheet or the like without any addition of a coloring agent, the resulting formed product is more or less discolored and such discoloration, called initial discoloration, is desired to be as slight as possible. However, the aforesaid coating film of the condensation product of an aromatic amine compound and an aromatic nitro compound may be peeled off or dissolved and then mixed in the polymeric product, thereby increasing the initial discoloration.
Furthermore, when the coating film of the condensation product of an aromatic amine compound and an aromatic nitro compound is formed, the condensation product is used as a coating liquid prepared by dissolving it in an organic solvent or a mixture of an organic solvent as the main component and water; therefore, the use of it is accompanied by danger of catching fire or explosion and a problem of safety in handling due to its toxicity.